**2. Comparison between IB values and histological images in carotid arteries**

Conventional echo images and IBS images were acquired using an ultrasonic imaging system (Sonos 5500, Philips Medical Systems) to characterize the carotid arterial tissue at the bedside conveniently using a 5-12 MHz multifrequency transducer for all studies. This software enabled the acquisition, storing and retrieving of a sequence of continuous 2D conventional and IB images, forming a continuous loop digital recording of two seconds (60 frames in two seconds). Off-line analysis of the 2D IBS images was performed by retrieving the previously stored data from the built-in optical disc drive in the system. IBS value was calculated as the average power of the ultrasound backscattered signal from a small volume of tissue measured in decibels (dB). We used an 11 x 11 pixels (0.6 mm x 0.6 mm) rectangle shaped ROI and set the time gain compensation at 0 dB and the lateral gain compensation at 50 dB at every measurement in both *ex vivo* and *in vivo* study. At this setting, IBS values of stainless steel at a distance of one to two centimeters from the transducer were 50 dB, which was within the dynamic range of the system. IBS values of the posterior arterial wall were corrected (corrected IBS) by subtracting the IBS values of the vessel lumen.

**Figure 1.** Integrated backscatter ultrasound color-coded maps of the carotid plaque. Left: color-coded maps (red: cal‐

Tissue Characterization of Carotid Plaques http://dx.doi.org/10.5772/57155 21

Several large clinical trials have demonstrated that lipid-lowering therapy with HMG-Co-A reductase inhibitors, (statins), reduces cerebrovascular events [10, 11]. Stabilization of vulner‐ able plaques rather than regression of plaque volume is considered the major contributor to this beneficial effect (5). Stabilization of vulnerable plaques rather than regression of plaque

We assessed the effect of a strong lipophilic statin (atorvastatin) on the stabilization of carotid plaques with ultrasound IBS color imaging by calculating the relative lipid volume. We enrolled patients who were diagnosed with asymptomatic carotid artery stenosis (30-60%) based on carotid ultrasonography and MR angiography. The patients were randomized to a statin (atorvastatin 20mg/day) treatment group (n = 20) or a diet group (n = 20). Transverse and longitudinal scans of carotid plaques were performed using an ultrasound imaging system (SONOS 7500, Philips Medical Systems). The plaques which have unstable component such as lipid core or necrotic core were also imaged with a 1.5-T magnetic resonance imaging (MRI) system (Intera Achieva Nova Dual, Philips Medical Systems) equipped with standard neck array coils. T1-weighted (T1W), proton density-weighted (PDW), and T2-weighted (T2W) images as well as time-of-flight (TOF) images of the plaques were obtained by standardized protocol. The components of plaque were assessed using previous established criteria [12]. We calculated the ratio of the signal intensity of carotid plaques to that of sternocleidomastoid

At baseline, clinical parameters did not differ between groups. After initiating statin therapy, the lipid profile significantly improved in the statin group, but remained unchanged in the diet group. Baseline IBS values and other characteristics and parameters were similar between the study groups. At baseline, no significant differences were found in these parameters between the statin and diet groups. The relative lipid volume significantly increased in the statin group after 6 months (Figure 2). However, IBS values did not change significantly in the

cification, orange: mixed lesion, green: fibrosis, blue: lipid pool). Right: pathological specimen.

**3. Effects of statin on carotid atherosclerotic plaques**

volume is considered the major contributor to this beneficial effect [3].

muscle and defined this as the signal intensity ratio (SIR).

diet group.

Carotid arteries were excised at autopsy and were fixed with 10% neutral buffered formalin. Ring-like arterial specimens obtained at a similar level to the ultrasound study were decalcified in a standard K-CX solution for five hours, and were embedded with paraffin and cut into 4 µm thick transverse sections perpendicular to the longitudinal axis of the artery. They were stained with hematoxylin-eosin, elastic van Gieson and Masson's trichrome. In addition, immunohistochemical analysis using anti-actin antibody was performed for detection of smooth muscle cells.

Histology of these sampling sites was divided into thrombus (n=5), lipid pool (n=31), intimal hyperplasia (n=7), fibrosis (n=25), mixed lesion (n=12) and calcification (n=17) in the intima, and the media (n=24). Each corrected IBS value of these tissues after fixation at autopsy was 7.3 ± 1.5, 13.0 ± 3.2, 10.9±1.0, 19.3 ± 2.4, 28.2 ± 3.3 and 39.3 ± 3.6 in the intima, respectively, and 11.3 ± 1.9 dB in the media. Also each corrected IBS value during lifetime was 4.9 ± 1.0, 10.0 ± 2.4, 8.0±0.8, 16.0 ± 2.0, 23.5 ± 3.4 and 30.5 ± 2.5 in the intima, respectively, and 8.4 ± 1.8 dB in the media. The difference among thrombus, fibrosis (category-3), mixed lesion, calcification and lipid pool, intimal hyperplasia or media were statistically significant. However, lipid pool, intimal hyperplasia and media had similar IBS values (category-2) [9]. In category-2, the media and intima were differentiated using conventional 2DE. Generally, the lipid pool (category-2) is anatomically located under a fibrous cap consisting of fibrosis (category-3). Therefore, the presence of ROIs with category-2 under a layer of ROIs with category-3 was defined as the lipid pool, but not as intimal hyperplasia.

Based on the above definitions using *in vivo* 2DE and IBS color-coded maps of tissue characterizations were constructed in *in vivo* images. These also reflected the pathology well (Figure 1).

**Figure 1.** Integrated backscatter ultrasound color-coded maps of the carotid plaque. Left: color-coded maps (red: cal‐ cification, orange: mixed lesion, green: fibrosis, blue: lipid pool). Right: pathological specimen.
